It is actively discouraged to put "keywords" in the title of a question, especially since Stack Exchange starting put the most popular tag in front of the title (which is done for SEO).

In other words:

SQL Server - How can I prevent injection when using sp_executesql?

Should simply be:

How can I prevent injecting when using sp_executesql?

In that example, it's already pretty clear that the question is about SQL Server. Sometimes, though, it isn't clear what the question is about without looking at the tags. I have cheated a few times and done something like:

How can I reverse an array in assembly?

Rather than:

How can I reverse an array?

Many people don't do this, and as a result, when asking questions:

The "Related Questions" are far less useful than they could be, which increases the likelihood of duplicate questions being asked.

If the tags were put above the body text, users would likely fill them out before starting to type the body text, and the "Related Questions" feature could use the tags along with the title to show higher quality potential duplicates.

I wouldn't say that it is actively discouraged to put keywords in the title of a question. The title and tags are two different ways of describing the post - and they need not be mutually exclusive. If you're going out of your way to exclude a tag from a natural title, you're doing it wrong.
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Rebecca ChernoffFeb 13 '11 at 23:27

@rebecca Without looking for it, I have seen at least eight or nine "third-party" edits where the only change was to remove a keyword from the title of a post.
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Closure CowboyFeb 13 '11 at 23:29

Yeah, that sounds harmful. Tags shouldn't be forced into the title, but they shouldn't be forcefully excluded.
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Rebecca ChernoffFeb 13 '11 at 23:33

I find that writing the body helps me flesh out which tags I should be using, so I probably wouldn't be filling that one out first anyway. Further, just a simple set of tags won't narrow the question down much further than the title.

I'd actually like the suggested questions area to change based on all three areas - title, tags, and body. I think the body area will be most valuable.

But I'd still like it to appear just below the title, and have the tags after the body, so the layout isn't something I'm interested in changing, but I agree that the bahavior should be updated to include all possible information.

Would be really cool if a metric was created, similarity to another question, which would display a percentage of likelihood of being closed as a duplicate of the most relevant question. Figuring out how to measure that is non-trivial, but I think if this was even partially implemented not only would we eliminate a lot of duplicates, people would get their answers a lot faster.